Surface acoustic wave (SAW) filters are frequently used for radio frequency (RF) filtering in devices such as wireless communication systems, due to small chip size and low insertion loss. The performance of a SAW filter depends on the characteristics of the SAW propagated in a piezoelectric substrate. SAW filters having low temperature coefficients of frequency (TCF) result in greater temperature independence at frequencies near the center of the pass band of the device.
Buried metal SAW filters have been used, and have demonstrated high electromagnetic coupling (high bandwidth), but may not provide a satisfactory TCF. Other challenges of buried metal SAW filters include damage to the piezoelectric substrate during polishing or etching steps of fabrication, and difficulty controlling thickness of buried electrodes, which in turn affects the signal frequency transmitted by the SAW filter.